Process for preparing a latex based on polypyrrole and use of this latex to form a conducting film

ABSTRACT

Process for preparing a latex of polypyrrole in an aqueous reagent medium containing a ferric salt, a hydrolyzed polyvinyl acetate and a dodecyl sulphate. The films prepared with this conducting latex are homogeneous, adhere to metals and metallized glasses and have high conductivity.

BACKGROUND OF THE INVENTION

1. Field of the Background

The invention relates to a process for preparing a latex based onpolypyrrole, from which it is possible to obtain adherent homogeneousfilms in a wide range of thickness and having high conductivity.

2. Discussion of the Background

It has already been proposed, in British Patent Application 2,181,367,to prepare conducting films based on pyrrole by polymerizing pyrrole inan aqueous medium in the presence of a polyvinyl alcohol and a substancecapable of providing the property of conductivity, such as a ferriccompound or a persulphate.

Similarly, it has been proposed--in the document Journal of Colloid andInterface Science, Vol. 118, No. 2, August 1987, p. 410-416--to preparea water-stable latex based on polypyrrole by employing a technique ofpolymerization of pyrrole involving ferric chloride as an initiator anda partially hydrolized polyvinyl acetate as a stabiliser.

However, these processes lead to polymers having low conductivity. Thefilms obtained with these polymers are, in general, poorly homogeneousor adhere only weakly to metals, glasses and metallized glasses.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a process which nolonger has these drawbacks.

To this end, the invention relates to a process for preparing a latexbased on polymers of pyrrole or of a pyrrole derivative in an aqueousreaction medium comprising a ferric salt, a polyvinyl alcohol or aderivative of this alcohol and a codispersant agent.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Codispersant agent is understood to mean organic compounds capable ofgiving rise to anions. Among these compounds, organic compounds whichreact with the ferric salt present in the reaction medium, or which havealready reacted with a ferric salt before introduction into the reactionmedium, are preferred. In general, alkyl or aryl sulphates orsulphonates, acids such as benzoic acid, ammonium salts or alkali metalsalts such as ammonium or sodium laurate, trichloroacetate,phenylphosphonate or (glycerol 2-phosphate) are employed.

Compounds chosen from the following are usually employed:

benzoic, para- and meta-hydroxybenzoic, trifluoromethanesulphonic,benzenesulphonic, para-toluene sulphonic and dodecylbenzenesulphonicacids;

salts such as sodium salts of trifluoromethanesulphonic, lauric,trichloroacetic, phenylphosphonic, glycerol-2-phosphonic,octylsulphonic, pentadecylsulphonic, hexadecyl-sulphonic,polyvinylsulphonic, polystyrenesulphonic, para-toluenesulphonic,dodecylbenzenesulphonic, para-hydroxy benzenesulphonic,4-dimenthylaminobenzenesulphonic, 1,3-benzene-disul-phonic and dodecylsulphuric acids.

Preferably, compounds containing a dodecyl sulphuric sulphate group areemployed. It is especially preferable to employ sodium dodecyl sulphate.

In the reaction medium, a polyvinyl alcohol or a derivative of thisalchol such as, in particular, an acetate is employed also, as adispersant agent. A hydrolysed polyvinyl acetate is usually employed,and preferably a hydrolysed polyvinyl acetate having a degree ofhydrolysis of between 72 and 96% and an average molecular weight ofbetween 50,000 and 200,000. Good results have been obtained with ahydrolysed polyvinyl acetate having a degree of hydrolysis of between 86and 90% and an average molecular weight of between 100,000 and 140,000.

In the reaction medium, a ferric salt is employed also, as an oxidizingand doping agent, causing polymerization. In general, an organic orinorganic ferric salt is employed. Usually, a chloride, sulphate ornitrate is employed as an inorganic ferric salt, and compounds of thefollowing type are employed as an organic ferric salt: irontrichloroacetate, iron phenylphosphonate, iron (glycerol 2-phosphate),iron pentadecylsulphonate, iron hexadecylsulphonate, ironpolyvinylsulphonate, iron polystyrenesulphonate, irondodecylbenzenesulphonate, iron tosylate, iron trifluoromethanesulphonateand iron dodecyl sulphate. Preferably, ferric chloride is employed.

Finally, the reaction medium contains a pyrrole derivative, which isunderstood to mean pyrrole, N-methylpyrrole, pyrroles substituted at the3-position and mixtures of these compounds. Preferably, unsubstitutedpyrrole is employed.

The quantity of codispersant agent employed in the process according tothe invention can vary according to its chemical nature.

When sodium dodecyl sulphate is used, 0.01 to 7.5 moles per mole ofpyrrole monomer, usually 0.05 to 3 moles and preferably 0.1 to 2 moles,are generally employed. Good results have been obtained withconcentrations of between 0.3 and 1 moles of sodium dodecyl sulphate permole of pyrrole monomer.

The quantity of polyvinyl alcohol, or of the derivative of this alcohol,employed can vary within wide limits, and depends on its solubility inwater. When a hyydrolysed polyvinyl acetate is used, 0.1 to 8 g pergram, of pyrrole monomer, and usually 0.2 to 5 g are generally employed.Good results have been obtained with concentrations of between 0.3 and 2g of hydrolysed polyvinyl acetate per gram pyrrole monomer.

In order for the process to show a good yield, the quantity of ferricsalt to be employed is large. When ferric chloride is used, 0.3 to 3moles of ferric chloride are generally employed per mole of pyrrole.Good results have been obtained with concentrations of between 2 and 2.7moles of ferric chloride per mole of pyrrole.

The process according to the invention is preferably performed in anaqueous medium, but the quantity of water needed can vary within widelimits, and depends chiefly on the other components.

The process according to the invention can advantageously be carried outaccording to the following stages:

in a first stage, water, the ferric salt, the polyvinyl alcohol or thederivative of this alcohol and the codispersant agent are introducedinto the reactor to form the reaction medium;

in a second stage, pyrrole or the pyrrole derivative is added withstirring to this reaction medium in the presence of water.

The latex finally obtained after these two stages is concentrated bycentrifugation or ultrafiltration or by any known method. It is thenwashed with water. The concentrated latex is washed and then redispersedin an aqueous solution of polyvinyl alcohol or of a derivative of thisalcohol. This aqueous solution usually contains from 0.1 to 50 g ofpolyvinyl alcohol or of the derivative of this alcohol per 100 ml ofwater, and preferably from 0.5 to 10 g. In general, the chemicalcompound already used in the first stage is employed.

The temperature at which the process is carried out is generally between0° and 50° C., and preferably between 5° and 40° C., when working atatmospheric pressure.

The pressure at which the process is carried out is not in itselfcritical. It is generally between 0.1 and 10 bar, and is preferablyequal to atmospheric pressure.

The process according to the invention can be carried out in anyapparatus or any reactor permitting the combination of the workingconditions described above.

The present invention also relates to the use of the latex obtained toform a conducting film. In effect, the process according to theinvention makes it possible to obtain stable latices, composed ofconducting polymers, capable of forming adherent, homogeneous and highlyconductive films in a wide range of thickness.

The films obtained are homogeneous and, as a result, do not laminatespontaneously. It is hence possible to obtain very thin layers such as,in particular, submicronic layers, films of 0.2 to several tens ofmicrons, but also layers of several hundred microns.

The conducting polymers obtained can, in particular, be used as activeor passive electrode materials, a binding agent in electrodes,electromagnetic screening, components of batteries, accumulators orcapacitors, electrochemical and electrochromic devices, paints forelectromagnetic absorption and also, depending on the thickness of thefilms obtained, for display, for data recording and as materials forelectronic components and circuits.

The latices obtained according to the invention can be deposited on anysupport such as, in particular, glass, metals, metallized glasses, glassfibres, textiles plastics.

EXAMPLES

The invention is illustrated by the examples which follow.

COMPARATIVE EXAMPLES 1R, 2R, 3R AND 4R

150 ml of water, ferric chloride (FeCl₃.6 H₂ O) and polyvinyl acetate,88% hydrolysed and of average moleecular weight 120,000, are introducedinto a 500-ml round-bottomed flask; the quantities of these products arenoted in Table 1.

To the reaction medium thereby obtained, pyrrole, dissolved in 50 ml ofwater, is added dropwise and with stirring.

The flask is maintained for 2 hours at 20° C. The product obtained isspread on metallized glass (ITO glass) and on nickel, and then dried atroom temperature overnight.

After this drying, the film obtained is washed with ethanol one or moretimes until the ethanol is clear.

The characteristics of the films obtained are collated in Table 1: thefilms obtained are poorly homogeneous and have low adhesion, and theirconductivity is low.

                                      TABLE 1                                     __________________________________________________________________________    Products employed                                                                         Hydrolysed  Characteristics of the films obtained                 Example                                                                            FeCl.sub.3.6H.sub.2 O                                                                polyvinyl          Adhesion*   Thickness obtained                                                                         Conductivity          No.  (g)    acetate (g)                                                                         Pyrrole (g)                                                                         Homogeneity                                                                          to ITO glass                                                                         to nickel                                                                          only 1 spreading                                                                           (S ·                                                                 cm.sup.-1)            __________________________________________________________________________    1R   29.7   1     3     very poor                                                                            2A     2A   50           10.sup.-2 to 1        2R   17.2   1.2   1.6   very poor                                                                            2A     2A    6           0.3                   3R   32.1   2.25  3     poor   2A     2A   75           10.sup.-1             4R   95.1   6.75  9     poor   2A     2A   100          3 ×                                                                     10.sup.-3             __________________________________________________________________________     *The adhesion is measured according to ASTM standard D 335978A, which         employs a test with 3M Scotch tape no. 710 (American National Standard). 

COMPARATIVE EXAMPLES 5R AND 6R

150 ml of water, 29.7 g of ferric chloride FeCl₃.6 H₂ O and 1 g ofpolyvinyl acetate, 88% hydrolysed and of average molecular weight120,000, are introduced into a 500-ml round-bottomed flask, and 3 g ofpyrrole, dissolved in 50 ml of water, are then added dropwise and withstirring.

The flask is maintained for 2 hours at 20° C. The product obtained iscentrifuged for 30 minutes at 15,000 rpm and washed twice with water.

It is then dispersed

either in a solution of 2 g of 88% hydrolysed polyvinyl acetate in 100ml of water (ex. 5R);

or in a solution of 5.6 g of 88% hydrolysed polyvinyl acetate in 200 mlof water (ex. 6R).

The product obtained is spread on metallized glass (ITO glass) and onnickel and then dried at room temperature overnight.

The characteristics of the films obtained are collated in Table 2.

The films obtained show low conductivity.

                                      TABLE 2                                     __________________________________________________________________________                  Adhesion*   Thickness obtained after                                                                  Conductivity                            Example No.                                                                          Homogeneity                                                                          on ITO glass                                                                         on nickel                                                                          only 1 spreading (μm)                                                                  (S · cm.sup.-1)                __________________________________________________________________________    5R     good   4A     4A   50-100      0.09                                    6R     good   4A     4A   80          10.sup.-4                               __________________________________________________________________________     *The adhesion is measured according to ASTM Standard D 335978A, which         employs a test with 3M Scotch tape No. 710 (American National Standard)  

EXAMPLES 7 and 8

150 ml of water, 29.7 g of ferric chloride FeCl₃.6 H₂ O, 4 g ofpolyvinyl acetate, 88% hydrolysed and of average molecular weight120,000, and 6.3 g of sodium dodecyl sulphate are introduced into a500-ml round-bottomed flask.

3 g of pyrrole, dissolved in 50 ml of water, are then added dropwise andwith stirring.

The flask is maintained for 2 hours at 20° C.

The latex obtained is centrifuged for 30 minutes at 15,000 rpm andwashed twice with water.

It is then dispersed in a solution of 2 g of 88% hydrolysed polyvinylacetate in 100 ml of water for Example 7, and 2 g of 88% hydrolysedpolyvinyl acetate in 300 ml of water for Example 8.

The latex obtained is spread on metallized glass (ITO glass) and onnickel, and then dried at room temperature overnight.

The characteristics of the films obtained are collated in Table 3: thefilms obtained have high conductivity and good adhesion.

                                      TABLE 3                                     __________________________________________________________________________                  Adhesion*    Thickness obtained after                                                                  Conductivity                           Example No.                                                                          Homogeneity                                                                          to ITO to glass                                                                       to nickel                                                                          only 1 spreading (μm)                                                                  (S · cm.sup.-1)               __________________________________________________________________________    7      good   4A      4A   50-100      10                                     8      good   4A      4A   10          12                                     __________________________________________________________________________     *The adhesion is measured according to ASTM Standard D 335978A, which         employs a test with 3M Scotch tape No. 710 (American National Standard). 

We claim:
 1. A process for preparing a latex based on pyrrole or apyrrole derivative, the latex forming an electrically conductive filmupon drying, comprising the following operations:1) in a first stage,water a ferric salt, a polyvinyl alcohol or derivative of this alcoholand a codispersant agent are introduced into a reactor, to form areaction medium, wherein said codispersant is an organic compoundcapable of giving rise to anions selected from the group consisting ofalkyl sulphates, aryl sulphates, alkyl sulphonates and aryl sulphonates,and 2) in a second stage, pyrrole or the pyrrole derivative is added tothe reaction medium in the presence of water.
 2. Process according toclaim 1, wherein the latex obtained is concentrated, then washed withwater and then redispersed in an aqueous solution of polyvinyl alcoholor of a derivative of this alcohol.
 3. Process according to claim 1,wherein the codispersant agent employed is sodium dodecyl sulphate. 4.Process according to claim 3, wherein sodium dodecyl sulphate isemployed at concentrations of between 0.3 and 1 mole per mole of pyrrolederivative.
 5. Process according to claim 1 wherein the polyvinylalcohol derivative employed is a hydrolysed polyvinyl acetate. 6.Process according to claim 5, wherein the hydrolysed polyvinyl acetateis employed at concentrations of between 0.1 and 8 g per g of pyrrole.7. Process according to claim 1 wherein the ferric salt employed isferric chloride.
 8. Process according to claim 7, wherein ferricchloride is employed at concentrations of between 2 and 2.7 moles permole of pyrrole.
 9. A process for preparing a latex based on polymers ofpyrrole or a pyrrole derivative in an aqueous reaction medium comprisingthe sequential steps of forming a solution of water, a ferric salt, apolyvinyl alcohol or a polyvinyl alcohol derivative, and a codispersantagent, wherein said codispersant is an organic compound capable ofgiving rise to anions selected from the group consisting of alkylsulphates, aryl sulphates, alkyl sulphonates and aryl sulphonates,andadding the pyrrole or the pyrrole derivative to the solution.
 10. Theprocess according to claim 9, wherein the codispersant agent contains adodecyl sulphate group.
 11. The process defined in claim 1, wherein thecodispersant agent is an organic compound producing a dodecyl sulfateanion.
 12. A process for preparing a latex based on pyrrole, the latexforming an electrically conductive film upon drying, comprising thefollowing operations:1) in a first stage, water, ferric chloride, ahydrolyzed polyvinyl acetate, and sodium dodecyl sulphate are introducedinto a reactor, to form a reaction medium, and 2) in a second stage,pyrrole is added to the reaction medium in the present of water. 13.Process according to claim 12, wherein sodium dodecyl sulphate isemployed at concentrations of between 0.3 and 1 mole per mole ofpyrrole.
 14. Process according to claim 12, wherein the hydrolyzedpolyvinyl acetate is employed at concentrations of between 0.5 and 2 gper g of pyrrole.
 15. Process according to claim 12, wherein ferricchloride is employed at concentrations of between 2 and 2.7 moles permole of pyrrole.
 16. Process according to claim 12, wherein the latexobtained is concentrated, then washed with water and then redispersed inan aqueous solution of polyvinyl alcohol or of a derivative of thisalcohol.